The present invention relates to a web winding method for taking up a web such as a magnetic recording medium.
In a production line for manufacturing a magnetic recording medium, a non-magnetic support web is transported at a predetermined speed, and such as a magnetic layer is applied over the support web, and the magnetic layer is then dried. In some cases, a magnetic layer is evaporated onto the support web. Subsequently, the web coated with the magnetic layer is subjected to calendering.
A web winding apparatus is disposed in predetermined locations along the production line. The web winding apparatus winds the web in a rolled manner, and thus forms a web roll. For example, the web winding apparatus is disposed downstream of an apparatus for the calendering.
As shown in FIG. 6, in this web winding apparatus, a web 81 is fed, then a contact roller 70 gently presses the web 81 onto an outer peripheral surface of a web roll 80. By means of such a configuration, since air is not involved between the web 81 and the outer peripheral surface of the web roll 80, the web roll 80 forms a good shape.
In the example shown in FIG. 6, the contact roller 70 remains in a line contact with the web 81. Namely, a wrap angle of the web 81 makes close to 0xc2x0 with respect to the contact roller 70. Such as a rubber roller having an elastic surface is employed as the contact roller 70.
The contact roller 70 has to remain in a line contact with the web 81, however the contact roller 70 is deformed by contact pressure that presses the web 81 against the outer peripheral surface of a web roll 80. Namely, when the web 81 twines around the contact roller 70 (at a certain wrap angle), the web 81 is slightly susceptible to the influence of the deformation of the contact roller 70, as a result of that flaws or wrinkles arise in the surface of the web 81.
Therefore, in order to maintain the line contact, a layout of an idle roller etc. to be disposed at upstream of the contact roller 70 has to be considered, and a design of facilities is regulated.
An increase in the feeding speed of a web (e.g., 200 m/min or more) is recently needed. In this light, a certain wrap angle of the web with respect to the contact roller prevents occurrence of meandering of the web (which becomes noticeable at higher speed). Hence, there has been a desire for establishment of facility design and process condition, which leaves a condition of xe2x80x9cline contactxe2x80x9d off.
It is an object of the present invention to provide a web winding method, a web winding apparatus and a contact roller, which can conspicuously prevent occurrence of flaws or wrinkles in a web without involvement of a drop in productivity.
The present invention provides a web winding method comprising steps of: feeding a web having a thickness of 5 to 70 xcexcm at a speed of 200 to 1000 m/min; wrapping the web around a contact roller at a wrap angle of 45 to 180xc2x0, wherein a coefficient of friction of the contact roller at each axial end surface is lower than that at an axial center surface; pressing the web against an outer peripheral surface of a web roll by the contact roller; and taking up the web in a rolled manner.
Further, the present invention provides a web winding apparatus for wrapping a web which has a thickness of 5 to 70 xcexcm and is fed at a speed of 200 to 1000 m/min in a rolled manner, and producing a web roll therefrom, comprising: a contact roller for pressing the web against an outer peripheral surface of the web roll, having both end surfaces and a center surface therebetween in its axial direction, wherein each end surface has a coefficient of friction lower than that of the axial center surface; and a guide path for wrapping the web around the contact roller at a wrap angle of 45 to 180xc2x0.
The present invention may also provide a contact roller for pressing a web against an outer peripheral surface of a web roll, having both end surfaces and a center surface therebetween in its axial direction, wherein each end surface has a coefficient of friction lower than that of the axial center surface.
The problem can also be solved by a web winding method comprising steps of: feeding a web having a thickness of 5 to 70 xcexcm at a speed of 200 to 1000 m/min; wrapping the web around a contact roller at a wrap angle of 45 to 180xc2x0, having an inner layer and an outer layer, wherein hardness of the outer layer is greater than that of the inner layer; pressing the web against an outer peripheral surface of a web roll by the contact roller; and taking up the web in a rolled manner.
The problem can also be solved by a web winding apparatus for wrapping a web which has a thickness of 5 to 70 xcexcm and is fed at a speed of 200 to 1000 m/min in a rolled manner, and producing a web roll therefrom, comprising: a contact roller for pressing the web against an outer peripheral surface of the web roll, having an inner layer and an outer layer, wherein hardness of the outer layer is greater than that of the inner layer; and a guide path for wrapping the web around the contact roller at a wrap angle of 45 to 180xc2x0.
The problem can also be solved by a contact roller for pressing a web against an outer peripheral surface of a web roll, having an inner layer and an outer layer, wherein hardness of the outer layer is greater than that of the inner layer.
As the result of that the present inventors devoted themselves to consider, they found that, by disposing a coefficient of friction of the axial center surface of the contact roller, lower than that of the axial end surface thereof, a web was less susceptible to an adverse effect such as occurrence of flaws. Namely, even when the above-mentioned case that a contact roller has been deformed by the contact pressure, deformation of the web has been absorbed to each axial end of the web over a contact roller. Hence, even if the web is wrapped around the contact roller in a high feeding speed, the web is less susceptible to an adverse effect such as occurrence of flaws.
In this case, it is preferable that a contact roller has the maximum coefficient of friction at the axial center portion thereof, and the coefficient of friction is gradually decreased from the axial center to axial ends thereof. However, the present invention is not limited to such a structure. For example, the coefficient of friction of a roller surface may be changed in an axial direction of the roller in phase.
On the other hand, if the contact roller is formed of a double-layer structure having different degrees of hardness of materials, the contact roller deforms uniformly, so as to well respond to the web. Namely, even when the above-mentioned case that a contact roller is deformed by the contact pressure, deformation of the web is absorbed. Hence, even if the web is wrapped around the contact roller, in a high feeding speed, the web is less susceptible to an adverse effect such as occurrence of flaws.
In this case, there is no limitation particularly to an outer dimension of the contact roller and to dimensions of the inner and outer layers of the contact roller. However it is preferable to produce a relative difference of hardness between the inner and outer rubber layers, and to set the whole hardness of the rubber layers to a rubber hardness (HsA) of, e.g., about 35. Here, the rubber hardness is defined in that the hardness (HsA) is measured by the spring type hardness test (A type) defined in JIS (Japanese Industrial Standard).
Namely, it is preferable to set the outer rubber layer to a rubber hardness (HsA) of, e.g., about 40, which is a well known and common requirement. In addition, it is preferable to set the inner rubber layer to a rubber hardness (HsA) of about 20.
As a result of a further study by the present inventors, a superior result was obtained in the case of a so-called thin web having a thickness of 70 xcexcm or less by means of each of the methods.
This is the reason why the thin web has low rigidity, and the web can readily follow the deformation of the contact roller within the range of elasticity.
The reason of such a phenomenon is not definite. However, the phenomenon is noticeable in the range of feeding speed e.g., 20 m/min or higher, which has not been achieved conventionally.
Probably, the phenomenon is considered to be ascribable to the influence of behavior of involved air. A hydrodynamic approach to solve the phenomenon is still intensively underway.
In any event, as experimental facts, an improvement in a wrap angle, which has not been achieved conventionally can be achieved under a condition that:
(1) a web having a thickness of 70 xcexcm or less is wrapped at a speed of 200 m/min or more, and by means of
(2) setting the coefficient of friction of axial end surfaces of the contact roller lower than that of the axial center surface of the contact roller.
In addition, an improvement in a wrap angle, which has not been achieved conventionally, can also be achieved under a condition that:
(1) a web having a thickness of 70 xcexcm or less is wrapped at a speed of 200 m/min or more and by means of
(2) forming a contact roller so as to be a double-layer structure.
In addition, in each of the above two structures, general repeated tests are intensively performed under conditions, as follows; a winding speed is limited to the highest speed of 1000 m/min which can be effected stably under an industry-scale test; a web thickness is limited to a thickness of 5 xcexcm which is the lowest limit for an industry product and a wrap angle is limited to a range of 45 to 180 xc2x0 in the range of which the flexibility of equipment design can be ensured.